1. Field of the Invention
The present invention relates to a signature authentication device, a signature authentication method, and a computer program product for authenticating the identity of a true user by receiving a signature from the user.
2. Description of the Related Art
A signature hand-written by a person has been used as means for identifying the person for a long time. Recently, besides authentication means for identifying a person who uses a password on a computer, techniques are contemplated to identify the person by authenticating an input hand-written signature.
Hand-written signature authentication is typically used to permit only a person himself or herself to monitor or overwrite sensitive information written in a portable terminal such as a computer.
To authenticate a hand-written signature on a computer, for instance, a signature is input using a digitizer and a pen, and input coordinates, input time, and pen force are converted into electrical signals as computer-readable data. A computer then compares the data with hand-written signature data of the person already registered in a dictionary, calculates a score indicating a difference between the input hand-written signature data and the registered hand-written signature data, and identifies the person by referring to whether the score exceeds a predetermined threshold.
To pre-register data for use in signature authentication, the computer allows a user to write the user's signature on a digitizer a plurality of times, checks the degree of similarity between the plurality of signatures, produces a single piece of dictionary data based on the signatures similar to each other to some degree, and registers the data.
In one method of registration, a single signature selected from among the plurality of the input signatures is registered or in the other method of registration, the plurality of the input signatures are averaged and the average value is registered.
FIGS. 5A and 5B show registration and authentication processes of a signature in a conventional hand-written signature authentication device. FIG. 5A is a flow diagram for registering a signature in a dictionary in the hand-written signature authentication device, and FIG. 5B is a flow diagram for authentication of the signature.
The signature registration process is now discussed.
In step S501, a buffer for storing the trace of the handwriting on a digitizer and variables are initialized. The device waits for a signature input in step S502.
One signature is input and hand-written data is stored in step S503, and when the input cycle is complete, the process goes to step S504.
If the newly input signature is at least the second input signature, then in step S504 the newly input hand-written signature is compared with the already input signatures for matching.
If the input signatures are determined to be similar in step S505, then the process goes to step S506 assuming that the signature input at this time is complete.
If the device detects no similarity between the input signatures, then in step S505, the process loops back to step S502, prompting the user to input the signature again.
If the device determines in step S506 that a predetermined number of cycles (n cycles) from step S502 through step S505 has been completed, then the process goes to step S507. The device produces dictionary data to be referenced for the hand-written signature in step S507 and stores the dictionary data in a file in step S508. When it is determined in step S506 that the n cycles have not yet been completed, the process loops back to step S502 for further signature input.
The authentication process during authentication is now discussed.
The buffer and variables are initialized in step S511 and the device waits for the input of an authentication signature in step S512.
When the device detects the end of the input of the signature, authentication data is produced in step S513. The process goes to step S514.
In step S514, the device compares the reference dictionary data stored in the dictionary with the authentication data, thereby calculating a score indicating the degree of similarity.
If the score calculated in step S514 is higher than a score threshold predetermined in the hand-written signature authentication device in step S515, the process goes to step S516. The authentication is thus successful. If the calculated score is lower than the score threshold, the process goes to step S517. The authentication is thus unsuccessful.
The conventional methods have disadvantages when there are large variations in the hand-written signatures during the signature registration in the above device, the signature authentication device detects no similarity between the signatures, and prompts the user to sign repeatedly thereon. This inconveniences the user, and large variations in the handwriting may require endless registration cycles.